The present invention relates to the construction and manufacture of thin prestressed concrete panels useful for architectural cladding of buildings and other purposes.
Exterior cladding of a building is subjected to attacks from climatic conditions such as freeze-thaw cycles, moisture intrusion, ultra-violet rays, wind and seismic loading and sometimes vibration from traffic and other sources, amongst other things.
Precast concrete cladding systems have been used extensively on commercial buildings because of their durability and architectural appeal. However, precast concrete cladding, as used heretofore, is provided typically in heavy elements and its use has been limited to reinforced concrete or steel frame structures due to the load that it imposes on a building. Consequently, a building designed to carry the lateral and gravity loads imposed by the heavy concrete skin system is costly. Moreover, existing concrete panel systems are susceptible to permanent deformation from perpendicularly applied loads that create surface cracks in the tension face of the panel.
In accordance with the invention, concrete panels are prepared by casting panels of about 1.5 inch thickness or less, which contain prestressed tendons. The tendons are oppositely positioned between the mid-plane of the panel and each of the opposite faces and may be spaced either equidistantly or at different distances from the adjacent face, in spaced grids. The positioning of opposing tendons between the mid-plane and the opposite faces increases panel resilience and will effect return of a panel to its original shape after being flexurally deformed by loads imposed normal to its faces, such return being effected even if a crack has developed in the tension face of the panel.
It is, accordingly, an object of this invention to provide a prestressed concrete panel that is thin, light, durable and resilient.
Another object of the invention is to provide a prestressed concrete panel that may be field cut and easily installed on a structure.
Still another object of the invention is to provide an improved apparatus for casting prestressed concrete panels at a reduced cost.
The foregoing and other objects, features and advantages of the present invention are described further in the following detailed description, which proceeds with reference to the accompanying.